The present invention relates to surgical articulators.
The effectiveness of various therapeutic tools such as graspers, punches, curettes, and scrapers which are used to manipulate tissue during minimally invasive surgical procedures can be enhanced with the addition of an articulating segment (herein, an xe2x80x9carticulatorxe2x80x9d) mounted between the distal end of a positioning rod and the base of the tool.
Accordingly, systems have been devised for providing controllable articulation of such therapeutic tools in one or more directions when the therapeutic tool is mounted to the distal end of the delivery rod. Such articulators are typically steered (ie: deflected) to position the therapeutic tool adjacent to the desired tissue by means of control rods, cables or other actuation mechanisms located in a hand piece at a proximal end of the positioning rod.
Traditional means for providing articulation include devices comprising a multiplicity of annular rings which are interlinked together to form pivots which allow for flexure of the articulator assembly. Specifically, these pivots are oriented in a manner which creates one or more preferential bending planes. One drawback of this type of articulator design is that it can lack sufficient positional stability for precision tissue manipulation when mounted to the distal end of a positioning rod.
For example, modes of instability of such devices include torsional instability about its longitudinal axis (especially when deflected, as the moment arm increases with increased articulation), radial instability about the longitudinal axis, (including lateral instability in directions perpendicular to the preferred bending plane of the articulator), and axial instability along the longitudinal axis of the articulator body. Moreover, such annular ring designs are typically machined from separate stainless steel pieces which must be assembled to form the articulator assembly, with high material and labor costs.
In a number of existing systems, a first control wire is used to control the articulation of the device, (such as for deflecting the angle of a scraper or a pair of forceps from the longitudinal axis of the positioning rod), and a second control wire is used to control the operation of the device, (such as for opening and closing the jaws of a pair of forceps).
A common problem of such existing systems is xe2x80x9ccrosstalkxe2x80x9d in which attempts to control the degree of articulation by displacing the device""s articulation control wire results in displacement of the tool control wire, which results in tool operation, or vice versa. Consequently, when operating forceps for example, the forceps jaws will tend either to open or to close as the angle of articulation is varied. Conversely, when attempting to open or close the forceps jaws, the angle of articulation of the forceps will tend to change. This xe2x80x9ccrosstalkxe2x80x9d problem is undesirable since the surgeon may simply desire to open and close the forceps (thus grasping targeted tissue) while the forceps remain in a constant deflected position. Similarly, the surgeon may simply wish to articulate the angle of the forceps without either opening or closing their jaws, (such as when first approaching the target tissue).
In existing systems, articulators are typically constructed from soft plastics such as low durometer polyeurathanes in order to have sufficient bending flexibility. Unfortunately, the use of such soft plastics results in significant losses to the device""s positional stability. Specifically, the articulator tends to compress in the axial direction when the articulation control wire is tensioned to deflect the distal end of the articulator. Such unwanted axial compression results in positioning inaccuracies which further exacerbates crosstalk problems.
The present invention provides an articulation system for positioning various surgical tools during surgical procedures, and is especially useful in positioning surgical tools in minimally invasive surgical procedures.
In a preferred aspect, the present invention provides a controllable articulator which is preferably mounted between the distal end of a positioning rod and the base of the surgical tool. An advantage of the present invention is that the positioning rod (with the articulator and surgical tool attached thereon at its distal end) may be introduced into a patient through a percutaneous cannula in a minimally invasive surgical procedure. Accordingly, the present invention is well suited for use in any manner of a minimally invasive surgery, including, but not limited to, arthroscopy and minimally invasive spinal surgery.
In a first aspect, the present articulator system comprises a longitudinally extending body which may preferably be integrally formed from a single piece or block of material. For example, the present articulator may preferably be formed by injection molding or formed by Steriolithography (SLA). An advantage of the present articulator being integrally formed from a single piece of material is that labor and material costs are substantially reduced (as compared to existing articulation systems which must be assembled piece by piece from a number of separate components).
In one preferred aspect, the present articulator is fabricated from a relatively rigid and strong thermoplastic material, for example acetal. As will be explained, the novel shape and characteristics of the present articulator system allows it to exhibit excellent bending flexibility in a preferred bending plane, yet still be constructed of a sufficiently hard material to prevent axial compression, radial deflection in planes other than the preferred bending plane (including lateral deflection in a plane perpendicular to the preferred bending plane) and torsional deflection about the central axis of the articulator body. As such, the positioning of the present articulator can be very precisely controlled through various degrees of deflection.
The novel shape of the present articulator also offers many advantages in its fabrication. For example, when injection molding the present invention, a tool control wire lumen and an articulation control wire lumen can be formed without xe2x80x9ccore pinsxe2x80x9d being required in mold shut-offs as is typically necessary to carve out separate actuator wire and control wire lumens as a hot plastic is initially flowed through the mold.
An advantage of not requiring such xe2x80x9ccore pinsxe2x80x9d when injection molding the present articulator is that the present articulator can be fabricated to very small dimensions. When attempting to form small lumens in existing injection molded parts, the size of the lumens are typically limited to the minimum diameter and length of a core pin which can be passed through the mold. This is due to the fact that it is not possible to use a core pin which is too thin since its structure will be affected by the hot plastic surrounding it during the molding process.
In contrast, the present articulator can be formed within interlocking 2-piece mold shut-offs without requiring the insertion of core pins into the mold to carve out lumens for either of the articulation or tool(i.e.: actuation) control wires.
The present articulator preferably comprises a longitudinally extending body, having a plurality of transverse grooves extending inwardly from opposite lateral sides of the longitudinally extending body. The transverse grooves preferably extend inwardly from each of the opposite lateral sides of the device in an alternating manner along the length of the longitudinally extending body. As such, the alternating nature of the transverse grooves enables the articulator to be highly flexible in a single preferred bending plane, as will be explained.
Preferably, the transverse grooves extend farther into the articulator body from one side of the articulator than from the other. In such a case, the longer grooves will be disposed on an inner bending surface of the articulator and will be compressed together as the articulator deflects in a preferred bending plane and the shorter grooves will be disposed on an outer bending surface of the articulator and will spread apart to offer stress relief as the articulator is deflected. As will be explained, the depth and spacing of the transverse grooves will define a neutral bending axis through the articulator body.
The articulator body preferably further comprises a plurality of recesses extending inwardly from the opposite sides in an alternating manner along the length of the longitudinally extending body. Such a plurality of recesses projecting inwardly from the opposite sides of the articulator body together preferably define both an articulation control wire lumen and a tool control wire lumen.
Preferably, the tool control lumen is disposed collinear with the neutral bending axis of the articulator. An important advantage of having the tool control wire, (which is received in the tool control wire lumen), collinear with a neutral bending axis of the articulator is that the potential for crosstalk is eliminated. This is due to the fact that deflection of the articulator about its neutral bending axis will neither cause tension nor compression in the tool control wire. As such, the tool control may, for example, be used to open and close teeth on a gripping device unaffected by deflection of the articulator caused by tensioning or compressing the articulation control wire (disposed in the articulation control wire lumen running parallel to the tool control wire). As such, the surgeon may use forceps positioned at the distal end of the articulator to grasp tissue when the articulator is in an articulated (i.e.: deflected) position and then apply a load to the articulator by pulling on the tissue. By positioning the forceps jaw opening control wire along the neutral bending axis of the articulator, the articulator will maintain the deflected position and will not straighten out as the forceps jaw control wire slides through the articulator to open or close the forceps. Correspondingly, another advantage of the present invention is that by placing the tool control wire collinear with the neutral axis, axial loads on the tool control wire do not cause unintended deflections of the articulator.
The transverse grooves which extend partially across the longitudinally extending body in an alternating fashion offer the advantage of significant bending flexibility in a preferred bending plane. In a preferred aspect of the invention, the innermost ends of the transverse grooves are rounded to further relieve bending stresses when the articulator is deflected.
In one preferred aspect of the invention, the transverse grooves are spaced evenly apart along the length of the articulator. As such, the articulator bends with a uniform curvature along its length. In other preferred aspects of the invention, the spacing between the transverse grooves is varied such that the articulator bends with different arcs of curvature along its length. For example, the transverse grooves can be spaced closer together at the distal end of the articulator such that maximum deflection curvature occurs at the distal end of the articulator.
The novel shape of the present articulator makes it highly flexible in a preferred bending plane, yet highly resistant to loads in other directions. Specifically, the present articulator is resistant to lateral loads, (perpendicular to the plane of deflection), torsional loads, and axial loads, or any combination thereof.
In a preferred aspect, free floating tension/compression sleeves may optionally be placed in the tool and articulation control wire lumens over the tool and articulation control wires thus preventing the actuators from sliding thereby improving control feel by imparting further rigidity to the articulator. Preferably, such sleeves can be made of low coefficient of friction materials thereby reducing excessive actuation friction.
In another aspect of the present invention, the plurality of recesses projecting inwardly from the top and bottom of the device together define a large central lumen which is adapted to receive both the articulation control wire and the tool control wire therethrough. Such a large central lumen may optionally have a keyhole shape (in cross section) to assist in holding the tool control wire coincident with the neutral bending axis of the articulator, as will be explained.
In another aspect of the present invention, the recesses which extend inwardly from the opposite sides of the articulator body are eliminated. Instead, the articulation control wire lumen is formed as a series of spaced apart cylinders which pass between the transverse grooves extending from one side of the articulator body. The articulation control wire lumen thus formed opens fully into the transverse grooves which extend into one side of the articulator body. In this aspect of the invention, the tool control wire lumen (which is disposed collinear with the neutral bending axis) opens directly into the innermost ends of the transverse grooves which extend inwardly from both opposite sides of the articulator body.